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In GHC built the devel2 way, compiling the following source file through GHC causes a compiler panic:

f :: (Num Int => Num) () => ()
f = undefined

[1 of 1] Compiling Main             ( tmp/xxx.hs, tmp/xxx.o )
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.7.20130416 for x86_64-unknown-linux):
        ASSERT failed!
    file compiler/types/Type.lhs line 1623
    base:GHC.Num.Num{tc 2b} ghc-prim:GHC.Types.Int{(w) tc 3J} =>
    base:GHC.Num.Num{tc 2b}
    ghc-prim:GHC.Prim.*{(w) tc 34d}
    -> ghc-prim:GHC.Prim.Constraint{(w) tc 34s}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

However, if you try to compile the same file through GHCi, you get a panic message but without the important details:

Prelude> :load tmp/xxx.hs
[1 of 1] Compiling Main             ( tmp/xxx.hs, interpreted )
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.7.20130416 for x86_64-unknown-linux):
        ASSERT failed!
<<details unavailable>>

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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